Method for returning a movable part to the original point

Abstract

A method of returning a movable top guide to the original point as defined by a frame of a machine body. The method comprises the steps of first moving in one direction the top guide to the frame at a high speed, moving the opposite direction the top guide away from the frame at an intermediate speed for a prescribed length of time after an overrun switch set at a point a little beyond the original point is rendered non-conductive, moving in one direction the top guide to the frame at a low speed and stopping the movement of the top guide when the original point switch provided at the original point is rendered nonconductive.

What is claimed is: 
     
       1. A method for returning a movable part to the original point which comprises: a first step of moving a movable part in one direction to the original point at a first speed causing the movable part to stop at a point a little beyond the original point;   a second step of moving the movable part in the opposite direction away from the original point at a second speed lower than said first speed for a prescribed length of time causing the movable part to be slightly removed from the original point;   a third step of moving the movable part which has been moved away from said original point for said prescribed length of time to the original point at a third speed lower than said second speed and, thereby stopping the movable part at said original point; and,   providing an original point switch at the original point and an overrun switch at a point a little beyond the original point such that, in the first step, the movable part continues to move until the movable part contacts the overrun switch, and in the third step, the movable part continues its travel until the movable part contacts the original point switch.   
     
     
       2. A method according to claim 1 wherein the original point switch and the overrun switch are normally closed switches and are opened when contacted by the movable part. 
     
     
       3. An apparatus for returning a movable part to the original point which comprises: actuator means for moving the movable part in a first direction and a second direction;   an original point switch which is located at the original point;   an overrun switch which is located a little beyond the original point, such that the original switch is first contacted with the movable part and then the overrun switch is contacted with the movable part when the movable part is moved in the first direction; and,   returning means connected to said actuator means, original point switch, and overrun switch for moving said movable part in the first direction at a first speed, this movement continuing when the movable part contacts the overrun switch, next for moving said movable part in the second direction at a second speed lower than the first speed for a prescribed period of time, and then for moving said movable part in the first direction at a third speed lower than the second speed, this movement continuing until the movable part contacts the original point switch.   
     
     
       4. An apparatus according to claim 3, wherein said prescribed period of time is set such that the movable part can be returned to a point a little before the original point, after the movable part moves for said prescribed period of time. 
     
     
       5. An apparatus according to claim 3, wherein said original point switch and said overrun switch are both normally closed switches, and when the movable part contact the original point, said original point switch being opened and the movable part being stopped.